1. Field of the Invention
The present invention relates to a video signal processing apparatus and, more particularly, to a video signal processing apparatus for receiving a video signal in which scanning lines are interlaced and supplying a video signal corresponding to the line-interlaced video signal to a display device having a comparatively small number of displayable scanning lines.
2. Description of the Related Art
FIG. 1 is a block diagram of a conventional electronic camera provided with a liquid crystal display device for displaying an image. The electronic camera shown in FIG. 1 includes an image pickup part 11 composed of predetermined constituent elements such as a lens for gathering subject light and a solid-state image pickup element, such as a CCD, for converting the subject light into an electrical signal, a recording signal processing circuit 12 for converting an output signal from the image pickup part 11 into a predetermined recordable signal format, a recording medium 13, such as tape, disc or semiconductor memory, for recording a video signal representative of a picked-up image, a reproduced signal processing circuit 14 for converting a video signal recorded on the recording medium 13 into a predetermined signal format for output to the outside, such as the original signal format, an external output terminal 15 from which to output a reproduced video signal, a switch circuit 16 and switch control means 17.
When a recording mode is selected by the switch control means 17, the switch circuit 16 is connected to a terminal "a" and outputs a signal supplied from the recording signal processing circuit 12 in a signal format suitable for display, for example, a signal format conforming to a television signal format. Such signal is a video signal representative of an image picked up by the image pickup part 11. When a reproduction mode is selected by the switch control means 17, the switch circuit 16 is connected to a terminal "b" and outputs a signal supplied from the reproduced signal processing circuit 14 in a signal format suitable for display. Such signal is a video signal read from the recording medium 13. The electronic camera shown in FIG. 1 also includes a display signal processing circuit 18 for converting an output from the switch circuit 16 into a signal having a predetermined format available for display provided by a liquid crystal display device 19, and the liquid crystal display device 19 for displaying an image represented by an input signal.
The operation of the electronic camera having the above-described construction will be described below.
During the recording mode (photographing mode), a photographed subject image is converted into an electrical video signal by the image pickup part 11, and after this video signal has been converted into a signal having the predetermined signal format by the recording signal processing circuit 12, the signal is recorded on the recording medium 13. At this time, the switch circuit 16 is connected to the terminal "a" by the switch control means 17 so that the video signal supplied from the recording signal processing circuit 12 is applied to the display signal processing circuit 18. The display signal processing circuit 18 converts the video signal into a signal having the predetermined format available for display, and the liquid crystal display device 19 visually displays the signal. Thus, an observer can monitor the image which is presently being picked up.
During the reproduction mode, a video signal reproduced from the recording medium 13 is converted into a signal having the predetermined signal format by the reproduced signal processing circuit 14, and the signal is supplied from the external output terminal 15 to an external apparatus or the like. At this time, the switch circuit 16 is connected to the terminal "b" by the switch control means 17 so that the reproduced video signal supplied from the reproduced signal processing circuit 14 is applied to the display signal processing circuit 18. Thus, the reproduced video signal is visually displayed by the liquid crystal display device 19, so that the observer can monitor the image which is presently being reproduced.
The liquid crystal display device 19 used in the conventional electronic camera has a high degree of pixel density, but, because of technical or manufacturing limitations, in many liquid crystal display devices, the number of displayable horizontal scanning lines is 220 to 240 which is approximately half the number of effective horizontal scanning lines, i.e., 480, in the case of, for example, television signals of NTSC system. The liquid crystal display device 19 having such a construction is arranged to display one frame image in the following manner. Since the odd field image of the frame image has 240 effective horizontal scanning lines, the odd field image is first sequentially written to all of the 240 horizontal scanning lines of the liquid crystal display device 19 during the period of the odd field. Then, since the even field image of the frame image also has 240 effective horizontal scanning lines, the even field image is sequentially written to all of the 240 horizontal scanning lines of the liquid crystal display device 19 during the period of the even field. Accordingly, if the frame image is to be displayed by the liquid crystal display device 19, the odd field image and the even field image are written to the same horizontal scanning lines.
As is known, such a television signal of NTSC system is formed by interlaced scanning and the odd and even field images are deviating from each other by one horizontal scanning line. As a result, since these field images are written to the same horizontal scanning lines of the liquid crystal display device as in the case of the above-described conventional example, a displayed image will be vertically shaken at intervals of one field. In particular, when a still image is displayed, this problem conspicuously appears.